1. Field of the Invention
The present invention relates to a sintered ferrite body. More specifically, the present invention relates to a sintered ferrite body to be included as a main body in a laminated ferrite component with an internal conductor provided therein, and to a laminated ferrite component including such a sintered ferrite body.
2. Description of the Related Art
A sintered ferrite body is used as a main body of a laminated ferrite component such as a laminated inductor array, a laminated LC complex noise filter, a laminated LC complex noise filter array, or a laminated common mode choke coil. An internal conductor is provided inside of the main body. Silver or an alloy including silver is often used as an electroconductive component contained in the internal conductor.
When constructing a main body for a laminated ferrite component with the above-described sintered ferrite body, baking at a relatively high temperature must be performed in the baking step for obtaining a sintered ferrite body in order to fully achieve desired electrical characteristics that the sintered ferrite body can inherently provide. However, when a silver-containing internal conductor is formed as described above, baking at such a high temperature will allow the silver contained in the internal conductor to diffuse into the ferrite portion, with the result that the electrical properties of the laminated ferrite component are be deteriorated.
A conventional attempt to solve this problem has involved adding glass to a ferrite. Glass acts as an adjuvant in sintering and has an ability to decrease the sintering temperature of a ferrite. Accordingly, addition of glass makes it possible to perform the baking of a ferrite at a relatively low temperature by virtue of the decreased sintering temperature of the ferrite. As a result, the diffusion of silver into the ferrite portion can be prevented.
This conventional solution involving adding glass to a ferrite, for example, is disclosed in Japanese Unexamined Patent Application Publication 8-148338, which describes that a laminated chip inductor with a large inductance value and with a small variation in properties can be obtained by adding a borosilicate glass having a softening point of 600xc2x0 C. or less to a raw ferrite material.
However, a ferrite in general has a relatively low specific resistance. Therefore, insulation deterioration and migration of an internal conductor occurs when a specific voltage is applied for a long time to the laminated ferrite component thus obtained.
Regarding the effects on inhibiting insulation deterioration and migration of an internal conductor as described above, it is not sufficient that a borosilicate glass that is added to a raw ferrite material has a softening point of 600xc2x0 C. or less as described in Japanese Unexamined Patent Application Publication 8-148338.
On the other hand, it may be possible to add a large quantity of glass to a raw ferrite material in order to increase the specific resistance of a sintered ferrite body. However, in such a case, the shape required for a sintered ferrite body cannot be maintained, and properties inherent in a ferrite material are damaged during the baking step because of the softened glass.
In order to overcome the problems described above, preferred embodiments of the present invention provide a sintered ferrite body with a greatly improved specific resistance and other preferred embodiments provide a laminated ferrite component including such an improved sintered ferrite body in which insulation deterioration and migration in an internal conductor are prevented.
In order to overcome the above-described technical problems with conventional devices, various preferred embodiments of the present invention provide a sintered ferrite body with a glass portion located on the ferrite grain boundary. The body is obtained by baking a raw ferrite material and a glass which is added to the raw ferrite material, the content of the glass is about 0.1% by weight to about 30% by weight with respect to the raw ferrite material, and the glass has, as a single material, a specific resistance xcfx81 (xcexa9) of about 10 or greater in the log xcfx81 unit, and a softening point of about 400xc2x0 C. to about 700xc2x0 C.
In a sintered ferrite body according to various preferred embodiments of the present invention, an Ni system, an Nixe2x80x94Zn system, or an Nixe2x80x94Cuxe2x80x94Zn system ferrite is preferably used as the ferrite material.
According to preferred embodiments of the present invention, a laminated ferrite component includes a sintered ferrite body having the characteristics as described above and an internal conductor disposed inside the body.
The present invention is particularly preferably applicable to a laminated ferrite component having an internal conductor including silver.
Other features, elements, characteristics and advantages of the present invention will become more apparent from detailed description of the preferred embodiments below.